The instant invention relates to an apparatus for preparing the cutting edge of a cutting tool, such as a sintered ceramic insert, by forming a chamfer of precise dimension and orientation thereon.
It is frequently desirable to provide a chamfer along the cutting edge of a cutting tool in order to reduce stress concentration encountered during use, thereby preventing edge chipping and increasing tool life. The chamfer, or K-land, is defined by the angle it makes with the leading face of the cutting tool, and its width, i.e., the distance in the plane of the tool's leading face from the beginning of the chamfered portion thereon to the edge generated by the intersection of the chamfered portion and the end face of the tool.
The prior art teaches the forming of the chamfered edge by way of an intuitive process wherein the edge of a sample tool is slightly abraded on a grinding machine having tool guides that are preliminarily set by, perhaps, a garden-variety protractor. The resulting chamfer is checked with the aid of an optical comparator. The tool guides are repeatedly readjusted and the tool edge abraded until such time as satisfactory chamfer dimensions are obtained. There is no means for determining the width of the chamfer other than measuring the chamfer subsequent to an abrading operation. The resultant trial-and-error procedure is very imprecise, and chamfer results are not reproducible with any degree of precision. Still greater difficulty is encountered when trying to form compound chamfers on the cutting-tool edge. Moreover, it is inherently problematical to use trial and error to obtain a chamfer width where the reference point from which the width is to be measured is itself being abraded, as is the case where the cutting tool is provided with a non-zero end-relief angle.
The intuitive nature of such a prior art process produces an involved, labor-intensive, and yet quite imprecise, method of apparatus set-up, thereby lowering process flexibility while making low volume batch processing uneconomical. Precisely prepared cutting-tool edges can not be predictably obtained with prior art methods. Automation is not a practical alternative, as industry demand is typified by low quantity orders for custom chamfered tool bits.
It is to be noted that the abrading machine characteristically employed by prior art edge preparation methods comprises a grinding wheel whose abrading surface travels in the direction parallel to the cutting edge of the tool. While the parallel orientation of abrading surface travel and cutting-tool edge is reasonably well suited for the edge preparation of sintered carbide tool bits, the use of a perpendicular direction of abrading surface travel appears to be advantageous for chamfering ceramic cutting-tool inserts. Moreover, the parallel orientation of abrading surface travel and cutting-tool edge further complicates the generation of an accurate chamfer around the corners (nose radii) of the tool--particularly of inserts having small inscribed circle dimensions--since the locating surface available for supporting the tool during edge preparation is reduced due to the larger aperture required therein to permit protuberance of the machine's arcuate abrading surface.